Function save_binary_state 

pub fn save_binary_state(
    blockchain_db: &BlockchainDb,
    path: &Path,
) -> Result<(), PersistenceError>

Save the current BlockchainDb state to a binary file.

This extracts accounts (without code) and storage from the MemDb and serializes them with bincode for fast restoration. Bytecode is excluded and persisted separately to bytecodes.bin; the saved account info keeps only the code_hash.

Returns an error if serialization, parent-directory creation, or writing fails, so explicit flush callers can distinguish a successful save from a stale or missing on-disk cache.

The on-disk format carries magic bytes and a version number before the bincode payload. Unknown versions are treated as a cache miss rather than being migrated.